Liquid level indicators which employ a magnetized float generally employ one or more optical indicator elements triggered by the magnets in the float and/or another type of magnetic proximity sensor such as a magnetostrictive wire operating to produce a level signal in a readout device.
Prior art level indicators of the magnetic float type were generally not satisfactorily reliable in situations where high pressure surrounded the float and/or where the liquid carrying the float was of low density. Liquefied light hydrocarbons commonly exist as low density liquids in high pressure vessels in the petroleum and petrochemical industries and heretofore have not lent themselves well to level measurements with magnetic float devices.